In a semiconductor element or other device manufacturing process, as exposure devices for transferring a mask or reticle circuit pattern onto a wafer, those that use visible light or ultraviolet light are currently the main types. However, as semiconductor circuit patterns become ever denser, the dimensions of the smallest patterns are approaching the resolution limits of exposure using light of the wavelengths described above. As a result, exposure methods that use smaller wavelength vacuum ultraviolet rays (VUV) and X-rays, or electron beams, have gained attention. For example, an exposure method using vacuum ultraviolet rays and X-rays is described in Japanese Patent Application Laid-Open No. 05-198471.
Vacuum ultraviolet rays (VUV) and X-rays or electron beams experience low transmittance in the atmosphere, and therefore in exposure methods that use such light or beams, the exposure must be conducted within a high vacuum. As a result, carrying out alignment is also subjected to stringent limiting conditions. For example, the wafer that is the detection target object is placed inside a vacuum chamber, but the sensor that senses an alignment mark must be placed outside the vacuum chamber at an observation window in order to combat the effects of escaping gas. Therefore, there is a possibility that the optical axis of the alignment system optical system might be warped by deformation of the chamber housing and observation window due to the difference in pressure between the inside of the chamber and the outside of the chamber, thus leading to an alignment detection error.